Phosphatidylinositol 3-kinase-δ up-regulates L-type Ca2+ currents and increases vascular contractility in a mouse model of type 1 diabetes.

BACKGROUND AND
PURPOSE: Vasculopathies represent the main cause of morbidity and mortality in diabetes. Vascular malfunctioning in diabetes is associated with abnormal vasoconstriction and Ca(2+) handling by smooth muscle cells (SMC). Phosphatidylinositol 3-kinases (PI3K) are key mediators of insulin action and have been shown to modulate the function of voltage-dependent L-type Ca(2+) channels (Ca(V) 1.2). In the present work, we investigated the involvement of PI3K signalling in regulating Ca(2+) current through Ca(V) 1.2 (I(Ca,L) ) and vascular dysfunction in a mouse model of type I diabetes. EXPERIMENTAL APPROACH: Changes in isometric tension were recorded on myograph. Ca(2+) currents in freshly dissociated mice aortic SMCs were measured using the whole-cell patch-clamp technique. Antisense techniques were used to knock-down the PI3Kδ isoform. KEY RESULTS Contractile responses to phenylephrine and KCl were strongly enhanced in diabetic aorta independent of a functional endothelium. The magnitude of phenylephrine-induced I(Ca,L) was also greatly augmented. PI3Kδ expression, but not PI3Kα, PI3Kβ, PI3Kγ, was increased in diabetic aortas and treatment of vessels with a selective PI3Kδ inhibitor normalized I(Ca,L) and contractile response of diabetic vessels. Moreover, knock-down of PI3Kδin vivo decreased PI3Kδ expression and normalized I(Ca,L) and contractile response of diabetic vessels ex vivo. CONCLUSIONS AND IMPLICATIONS: Phosphatidylinositol 3-kinase δ was essential to the increased vascular contractile response in our model of type I diabetes. PI3Kδ signalling was up-regulated and most likely accounted for the increased I(Ca,L,) leading to increased vascular contractility. Blockade of PI3Kδ may represent a novel therapeutic approach to treat vascular dysfunction in diabetic patients.